U.S. patent number 4,788,332 [Application Number 07/145,786] was granted by the patent office on 1988-11-29 for l-aminodicarboxylic acid esters.
This patent grant is currently assigned to General Foods Corporation. Invention is credited to Ronald E. Barnett, Glenn M. Roy, Paul R. Zanno.
United States Patent |
4,788,332 |
Zanno , et al. |
November 29, 1988 |
L-aminodicarboxylic acid esters
Abstract
Sweeteners of the formula: ##STR1## and food-acceptable salts
thereof, where the substituents are disclosed herein.
Inventors: |
Zanno; Paul R. (Nanuet, NY),
Barnett; Ronald E. (Barrington, IL), Roy; Glenn M.
(Streamwood, IL) |
Assignee: |
General Foods Corporation
(White Plains, NY)
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Family
ID: |
26767249 |
Appl.
No.: |
07/145,786 |
Filed: |
January 19, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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82246 |
Aug 5, 1987 |
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898063 |
Aug 19, 1986 |
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723603 |
Apr 15, 1985 |
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Current U.S.
Class: |
562/498; 562/500;
562/501; 562/502; 562/503; 562/505; 562/506; 562/507 |
Current CPC
Class: |
C07K
5/06104 (20130101) |
Current International
Class: |
C07K
5/00 (20060101); C07K 5/072 (20060101); C07C
103/37 () |
Field of
Search: |
;562/498,500,501,502,503,505,506,507 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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168112 |
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Jan 1986 |
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EP |
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61-200999 |
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Sep 1986 |
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JP |
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61-291596 |
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Dec 1986 |
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JP |
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61-291597 |
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Dec 1986 |
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JP |
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Other References
"An Exploration on the Molecular Recognition of Sweet Taste with an
Induced Fit Model of Gustatory Receptor", Journal of Molecular
Science, Dec. 1981, vol. 2 (published in the People's Republic of
China). .
"Structure Sweetness Relationship of L-Aspartic Acid Dipeptides
published by Shanghai Institute of Organic Chemistry", J. of Org.
Chem. (Chinese), 16 (1982), People's Republic of China. .
"Molecular Discrimination in the Sense of Taste", Zeng Guangzhi,
Science Press, Beijing (Jul. 1984, People's Republic of
China)..
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Primary Examiner: Phillips; Delbert R.
Attorney, Agent or Firm: Grim; Linn I. Donovan; Daniel
J.
Parent Case Text
This is a continuation of application Ser. No. 082,246, filed
8/5/87, which in turn is a continuation-in-part of copending Ser.
No. 898,063, filed 8/19/86 and, which in turn, is a
continuation-in-part of Ser. No. 723,603, filed 4/15/85, now
abandoned.
Claims
What is claimed is:
1. A compound represented by the Formula: ##STR27## and
food-acceptable salts thereof, including a food acceptable salt of
N-L-aspartyl-D-alanine[.beta.(+)fenchyl]ester and a food acceptable
salt of N-L aspartyl-2-methylalanine[.beta.(+)fenchyl]ester
wherein
A is hydrogen, and alkyl containing 1-3 carbon atoms,
A' is hydrogen or alkyl containing 1-3 carbon atoms;
alternatively
A and A' taken together with the carbon atom to which they are
attached form cycloalkyl containing 3-4 carbon atoms;
Y is --(CHR.sub.2).sub.n --R.sub.1 or --CHR.sub.3 R.sub.4 ;
R.sub.1 is a .beta.,.beta.-dialkyl cycloalkyl, a
.beta.,.beta.'-dialkyl cycloalkyl, a .beta.,.beta.,.beta.'-trialkyl
cycloalkyl, .beta.,.beta.,.beta.',.beta.'-tetraalkyl cycloalkyl on
which the alpha substituent is hydrogen and wherein the cycloalkyl
ring contains up to 6 ring carbon atoms and a total of 12 carbon
atoms;
with the proviso that when the double asterisked carbon is an
asymmetric or chiral center, the configuration around said carbon
is in the D form.
2. A compound according to claim 1 wherein 1 R.sub.1 is an
alkyl-substituted cyclopentyl or cyclohexyl containing a total of
up to 10 carbon atoms.
3. A compound according to claim 1 wherein n=0.
4. A compound according to claim 1 wherein R.sub.1 is mono-, di-,
tri- or tetramethyl cycloalkyl containing up to 10 carbon
atoms.
5. A compound according to claim 4 wherein R.sub.1 is a
.beta.,.beta.-dimethyl-substituted cycloalkyl.
6. A compound according to claim 4 wherein R.sub.1 is a
.beta.,.beta.'-dimethyl-substituted cycloalkyl.
7. A compound according to claim 4 where R.sub.1 is a
.beta.,.beta.,.beta.'-trimethyl-substituted cycloalkyl.
8. A compound according to claim 4 wherein R.sub.1 is a
.beta.,.beta.,.beta.',.beta.'-tetramethyl-substituted
cycloalkyl.
9. A compound according to claim 1 wherein R.sub.3 and R.sub.4 are
cyclopropyl.
10. A compound represented by the formula: ##STR28## and
food-acceptable salts thereof, wherein A is hydroxyalkyl containing
1-3 carbon atoms or alkoxymethyl wherein the alkoxy contains 1-3
carbon atoms;
A' is hydrogen or alkyl containing 1-3 carbon atoms;
alternatively
A and A' taken together with the carbon atom to which they are
attached form cycloalkyl containing 3-4 carbon atoms;
Y is --(CHR.sub.2).sub.n --R.sub.1 or --CHR.sub.3 R.sub.4 ;
R.sub.1 is an alkyl-substituted cycloalkyl, cycloalkenyl
bicycloalkyl or bicycloalkenyl wherein at least one alkyl is in the
.beta.-position of the cycloalkyl, cycloalkenyl, bicycloalkyl or
bicycloalkenyl ring, containing up to 7 ring carbon atoms and a
total of 12 carbon atoms;
R.sub.2 is H or alkyl containing 1-4 carbon atoms;
R.sub.3 and R.sub.4 are each cycloalkyl containing 3-4 ring carbon
atoms;
n=0 or 1; and
m=0 or 1,
with the proviso that when the double asterisked carbon is an
asymmetric or chiral center, the configuration around said carbon
is in the D form.
11. A compound according to claim 10 wherein R.sub.1 is an
alkyl-substituted cyclopentyl or cyclohexyl containing a total of
up to 10 carbon atoms.
12. A compound according to claim 10 wherein n=0.
13. A compound according to claim 10 wherein R.sub.1 is mono-, di-,
tri- or tetramethyl cycloalkyl or bicycloalkyl containing up to 10
carbon atoms.
14. A compound according to claim 13 wherein R.sub.1 is a
.beta.-methyl-substituted cycloalkyl or bicycloalkyl.
15. A compound according to claim 13 wherein R.sub.1 is a
.beta.,.beta. or .beta.,.beta.'-dimethyl-substituted cycloalkyl or
bicycloalkyl.
16. A compound according to claim 13 wherein R.sub.1 is a
.beta.,.beta.,.beta.'-trimethyl-substituted cycloalkyl or
bicycloalkyl.
17. A compound according to claim 13 wherein R.sub.1 is a
.beta.,.beta.,.beta.',.beta.'-tetramethyl-substituted cycloalkyl or
bicycloalkyl.
18. A compound according to claim 10 wherein R.sub.3 and R.sub.4
are cyclopropyl.
19. A compound represented by the formula: ##STR29## and
food-acceptable salts thereof, wherein A is hydroxyalkyl containing
1-3 carbon atoms;
A' is hydrogen or alkyl containing 1-3 carbon atoms;
Y is --(CHR.sub.2).sub.n --R.sub.1 or --CHR.sub.3 R.sub.4 ;
R.sub.1 is an alkyl-substituted cycloalkyl, cycloalkenyl
bicycloalkyl or bicycloalkenyl wherein at least one alky is in the
.beta.-position of the cycloalkyl, cycloalkenyl, bicycloalkyl or
bicycloalkenyl ring, containing up to 7 ring carbon atoms and a
total of 12 carbon atoms;
R.sub.2 is H or alkyl containing 1-4 carbon atoms;
R.sub.3 and R.sub.4 are each cycloalkyl containing 3-4 ring carbon
atoms;
n=0 or 1; and
m=0 or 1,
with the proviso that when the double asterisked carbon is an
asymmetric or chiral center, the configuration around said carbon
is in the D form.
20. A compound according to claim 19 wherein R.sub.1 is an
alkyl-substituted cyclopentyl or cyclohexyl containing a total of
up to 10 carbon atoms.
21. A compound according to claim 19 wherein n=0.
22. A compound according to claim 19 wherein R.sub.1 is mono-, di-,
tri- or tetramethyl cycloalkyl or bicycloalkyl containing up to 10
carbon atoms.
23. A compound according to claim 22 wherein R.sub.1 is a
.beta.-methyl-substituted cycloalkyl or bicycloalkyl.
24. A compound according to claim 22 wherein R.sub.1 is a
.beta.,.beta. or .beta.,.beta.'-dimethyl-substituted cycloalkyl or
bicycloalkyl.
25. A compound according to claim 22 wherein R.sub.1 is a
.beta.,.beta.,.beta.'-trimethyl-substituted cycloalkyl or
bicycloalkyl.
26. A compound according to claim 22 wherein R.sub.1 is a
.beta.,.beta.,.beta.',.beta.'-tetramethyl-substituted cycloalkyl or
bicycloalkyl.
27. A compound according to claim 19 wherein R.sub.3 and R.sub.4
are cyclopropyl.
28. A compound represented by the formula: ##STR30## and
food-acceptable salts thereof, wherein A is alkoxymethyl wherein
the alkoxy contains 1-3 carbon atoms;
A' is H or alkyl containing 1-3 carbon atoms;
Y is --(CHR.sub.2).sub.n --R.sub.1 or --CHR.sub.3 R.sub.4 ;
R.sub.1 is an alkyl-substituted cycloalkyl, cycloalkenyl
bicycloalkyl or bicycloalkenyl wherein at least one alky is in the
.beta.-position of the cycloalkyl, cycloalkenyl, bicycloalkyl or
bicycloalkenyl ring, containing up to 7 ring carbon atoms and a
total of 12 carbon atoms;
R.sub.2 is H or alkyl containing 1-4 carbon atoms;
R.sub.3 and R.sub.4 are each cycloalkyl containing 3-4 ring carbon
atoms;
n=0 or 1; and
m=0 or 1,
with the proviso that when the double asterisked carbon is an
asymmetric or chiral center, the configuration around said carbon
is in the D form.
29. A compound according to claim 28 wherein R.sub.1 is an
alkyl-substituted cyclopentyl or cyclohexyl containing a total of
up to 10 carbon atoms.
30. A compound according to claim 28 wherein n=0.
31. A compound according to claim 28 wherein R.sub.1 is mono-, di-,
tri- or tetramethyl cycloalkyl or bicycloalkyl containing up to 10
carbon atoms.
32. A compound according to claim 31 wherein R.sub.1 is a
.beta.-methyl-substituted cycloalkyl or bicycloalkyl.
33. A compound according to claim 31 wherein R.sub.1 is a
.beta.,.beta. or .beta.,.beta.'-dimethyl-substituted cycloalkyl or
bicycloalkyl.
34. A compound according to claim 31 wherein R.sub.1 is a
.beta.,.beta.,.beta.'-trimethyl-substituted cycloalkyl or
bicycloalkyl.
35. A compound according to claim 31 wherein R.sub.1 is a
.beta.,.beta.,.beta.',.beta.'-tetramethyl-substituted cycloalkyl or
bicycloalkyl.
36. A compound according to claim 28 wherein R.sub.3 and R.sub.4
are cyclopropyl.
37. A compound represented by the formula: ##STR31## and
food-acceptable salts thereof, wherein A and A' taken together with
carbon atom to which they are attached form a cycloalkyl containing
3-4 carbon atoms;
Y is --(CHR.sub.2).sub.n --R.sub.1 or --CHR.sub.3 R.sub.4 ;
R.sub.1 is an alkyl-substituted cycloalkyl, cycloalkenyl
bicycloalkyl or bicycloalkenyl wherein at least one alky is in the
.beta.-position of the cycloalkyl, cycloalkenyl, bicycloalkyl or
bicycloalkenyl ring, containing up to 7 ring carbon atoms and a
total of 12 carbon atoms;
R.sub.2 is H or alkyl containing 1-4 carbon atoms;
R.sub.3 and R.sub.4 are each cycloalkyl containing 3-4 ring carbon
atoms;
n=0 or 1; and
m=0 or 1,
with the proviso that when the double asterisked carbon is an
asymmetric or chiral center, the configuration around said carbon
is in the D form.
38. A compound according to claim 37 wherein R.sub.1 is an
alkyl-substituted cyclopentyl or cyclohexyl containing a total of
up to 10 carbon atoms.
39. A compound according to claim 37 wherein n=0.
40. A compound according to claim 37 wherein R.sub.1 is mono-, di-,
tri- or tetramethyl cycloalkyl or bicycloalkyl containing up to 10
carbon atoms.
41. A compound according to claim 40 wherein R.sub.1 is a
.beta.-methyl-substituted cycloalkyl or bicycloalkyl.
42. A compound according to claim 40 wherein R.sub.1 is a
.beta.,.beta. or .beta.,.beta.'-dimethyl-substituted cycloalkyl or
bicycloalkyl.
43. A compound according to claim 40 wherein R.sub.1 is a
.beta.,.beta.,.beta.',.beta.'-tetramethyl-substituted cycloalkyl or
bicycloalkyl.
44. A compound according to claim 37 wherein R.sub.3 and R.sub.4
are cyclopropyl.
45. The compound according to claim 1 which is
N-L-Aspartyl-D-alanine (2,2,5,5-tetramethylcyclopentyl) ester.
46. The compound according to claim 1 which is
N-L-Aspartyl-D-alanine (2,2,5-trimethylcyclclopentyl) ester.
47. The compound according to claim 1 which is
N-L-Aspartyl-D-alanine (2,5-dimethylcyclopentyl) ester.
48. The compound according to claim 1 which is
N-L-Aspartyl-D-alanine (dicyclopropylmethyl) ester.
49. The compound according to claim 1 which is a food acceptable
salt of N-L-Aspartyl-D-alanine[.beta.(+)fenchyl]ester.
50. The compound according to claim 1 which is
N-L-Aspartyl-2-methylalanine (2,2,5,5-tetramethylcyclopentyl)
ester.
51. The compound according to claim 1 which is
N-L-Aspartyl-2-methylalanine (2,2,5-trimethylcyclopentyl)
ester.
52. The compound according to claim 1 which is
N-L-Aspartyl-2-methylalanine (2,5-dimethylcyclopentyl) ester.
53. The compound according to claim 1 which is
N-L-Aspartyl-2-methylalanine (dicyclopropylmethyl) ester.
54. The compound according to claim 1 which is a food acceptable
salt of N-L-Aspartyl-2-methylalanine[.beta.(+)fenchyl]ester.
55. The compound according to claim 10 which is
N-L-Aspartyl-D-serine (2,2,5,5-tetramethylcyclopentyl) ester.
56. The compound according to claim 10 which is
N-L-Aspartyl-D-serine (2,2,5-trimethylcyclopentyl) ester.
57. The compound according to claim 10 which is
N-L-Aspartyl-D-serine (2,5-dimethylcyclopentyl) ester.
58. The compound according to claim 10 which is
N-L-Aspartyl-D-serine (dicyclopropylmethyl) ester.
59. The compound according to claim 10 which is
N-L-Aspartyl-D-serine (fenchyl) ester.
60. The compound according to claim 10 which is
N-L-Aspartyl-D-serine[.beta.(+)fenchyl]ester.
61. The compound according to claim 10 which is
N-L-aspartyl-D-serine (2-t-butylcyclopentyl) ester.
62. The compound according to claim 10 which is
N-L-Aspartyl-D-serine (1-t-butyl-1-cyclopropylmethyl) ester.
63. The compound according to claim 10 which is
N-L-Aspartyl-D-serine (1-isopropyl-1-cyclopropylmethyl) ester.
64. The compound according to claim 10 which is
N-L-Aspartyl-O-methyl-D-serine (2,2,5,5-tetramethylcyclopentyl)
ester.
65. The compound according to claim 10 which is
N-L-Aspartyl-O-methyl-D-serine (2,2,5-trimethylcyclopentyl)
ester.
66. The compound according to claim 10 which is
N-L-Aspartyl-O-methyl-D-serine (2,5-dimethylcyclopentyl) ester.
67. The compound according to claim 10 which is N-L-Aspartyl
O-methyl-D-serine dicyclopropylmethyl) ester.
68. The compound according to claim 10 which is N-L-Aspartyl
O-methyl-D-serine (fenchyl) ester.
69. The compound according to claim 10 which is
N-L-Aspartyl-O-methyl-D-serine[.beta.(+)fenchyl]ester.
70. The compound according to claim 10 which is N-L-Aspartyl
O-methyl-D-serine (2-t-butylcyclopentyl) ester.
71. The compound according to claim 10 which is N-L-Aspartyl
O-methyl-D-serine (1-t-butyl-1-cyclopropylmethyl) ester.
72. The compound according to claim 10 which is N-L-Aspartyl
O-methyl-D-serine (1-isopropyl-1-cyclopropylmethyl) ester.
73. The compound according to claim 37 which is
N-L-Aspartyl-1-aminocyclopropane-1-carboxylic acid
(2,2,5,5-tetramethylcyclopentyl) ester.
74. The compound according to claim 37 which is N-L-aspartyl
1-aminocyclopropane-1-carboxylic acid (2,2,5-trimethylcyclopentyl)
ester.
75. The compound according to claim 37 which is N-L-aspartyl
1-aminocyclopropane-1-carboxylic acid (dicyclopropylmethyl)
ester.
76. The compound according to claim 37 which is N-L-aspartyl
1l-aminocyclopropane-1-carboxylic acid (fenchyl) ester.
77. The compound according to claim 37 which is
N-L-aspartyl-1-aminocyclopropane-1-carboxylic acid
(2-t-butylcyclopentyl) ester.
78. The compound according to claim 37 which is N-L-aspartyl
1-aminocyclopropane-1-carboxylic acid
(1-t-butyl-1-cyclopropylmethyl) ester.
79. The compound according to claim 37 which is N-L-aspartyl
1-aminocyclopropane-1-carboxylic acid
(1-isopropyl-1-cyclopropyl-methyl) ester.
Description
This invention relates to a novel group of compounds and more
particularly to a novel group of compounds particularly well suited
as sweeteners in edible foodstuff.
Sweetness is one of the primary taste cravings of both animals and
humans. Thus, the utilization of sweetening agents in foods in
order to satisfy this sensory desire is well established.
Naturally occurring carbohydrate sweeteners such as sucrose, are
still the most widely used sweetening agents. While thse naturally
occurring carbohydrates, i.e., sugars, generally fulfill the
requiremenets of sweet taste, the abundant usage thereof does not
occur without deleterious consequence, e.g., high caloric intake
and nutritional imbalance. In fact, oftentimes the level of these
sweeteners required in foodstuffs is far greater than the level of
the sweetener that is desired for economic, dietetic or other
functional consideration.
In an attempt to eliminate the disadvantages concomitant with
carbohydrate sweeteners, considerable research and expense have
been devoted to the productio of artificial sweeteners, such as for
example, saccharin, cyclamate, dihydrochalcone, aspartame, etc.
While some of these artificial sweeteners satisfy the requirements
of sweet taste without caloric input, and have met with
considerable commercial success, they are not, however, without
their own inherent disadvantages. For example, many of these
artificial sweeteners have the disadvantages of high cost, as well
as delay in the preception of the sweet taste, persistant lingering
of the sweet taste, and very objectionable bitter, metallic
aftertaste when used in food products.
Since it is believed that many disadvantages of artificial
sweeteners, particularly aftertaste, is a function of the
concentration of the sweetener, it has been previously suggested
that these effects could be reduced or eliminated by combining
artificial sweeteners such as saccharin, with other ingredients
such as aspartame or natural sugars, such as sorbitol, dextrose,
maltose, etc. These combined products, however, have not been
entirely satisfactory either. Some U.S. Patents which disclose
sweetener mixtures include for example, U.S. Pat. No. 4,228,198;
U.S. Pat. No. 4,158,068; U.S. Pat. No. 4,154,862; and U.S. Pat. No.
3,717,477.
Accordingly, much work has continued in an attempt to develop and
identify compounds that have a sweet taste and which will satisfy
the need for better lower calorie sweeteners, and so research
continues for sweeteners that have intense sweetness, that is,
deliver a sweet taste at low use levels and which will also produce
enough sweetness at higher levels to act as sole sweetener for most
sweetener applications. Furthermore, the sweeteners sought must
have good temporal and sensory qualities. Sweeteners with good
temporal qualities produce a time-intensity sweetness response
similar to carbohydrate sweeteners without lingering. Sweeteners
with good sensory qualities lack undesirable off tastes and
aftertaste. Furthermore, these compounds must be economical and
safe to use.
In U.S. Pat. No. 3,798,204, L-aspartyl-O-t-butyl-L-serine methyl
ester and L-aspartyl-O-t-amyl-L-serine methyl ester are described
as sweet compounds having significant sweetness.
In U.S. Pat. No. 4,448,716 metal complex salts of dipeptide
sweeteners are disclosed. In the background of this patent a
generic formula is described as an attempt to represent dipeptide
sweeteners disclosed in five prior patents: U.S. Pat. No.
3,475,403; U.S. Pat. No. 3,492,131; Republic of South Africa Pat.
No. 695,083 published July 10, 1969; Republic of South African Pat.
No. 695,910 published Aug. 14, 1969; and German Pat. No. 2,054,554.
The general formula attempting to represent these patents is as
follows: ##STR2##
wherein R represents the lower alkyls, lower alkylaryls and
cycloalkyls, n stands for integers 0 through 5, R.sub.1 represents
(a) phenyl group, (b) lower alkyls, (c) cycloalkyls, (d)
R.sub.2.
Where R.sub.2 is hydroxy, lower alkoxy, lower alkyl, halogen, (e)
(S(O).sub.m (lower alkyl) where m is 0, 1 or 2 and provided n is 1
or 2, (f) R.sub.3.
Where R.sub.3 represents hydroxy or alkoxy and (g) single or double
unsaturated cycloalkyls with up to eight carbons. These compounds
also are not entirely satisfactory in producing a high quality
sweetness or in producing a sweet response at lower levels of
sweetener.
Dipeptides of aspartyl-cysteine and aspartylmethionine methyl
esters are disclosed by Brussel, Peer and Van der Heijden in
Chemical Senses and Flavour, 4, 141-152 (1979) and in Z. Lebensm.
Untersuch-Forsch., 159, 337-343 (1975). The authors disclose the
following dipeptides:
In U.S. Pat. No. 4,399,163 to Brennan et al., sweeteners having the
following formulas are disclosed: ##STR3## and physiologically
acceptable cationic and acid addition salts thereof wherein
R.sup.a is CH.sub.2 OH or CH.sub.2 OCH.sub.3 ;
R is a branched member selected from the group consisting of
fenchyl, diisopropylcarbinyl, d-methyl-t-butylcarbinyl,
d-ethyl-t-butyl-carbinyl, 2-methylthio-2,4-dimethylpentan-3-yl,
di-t-butyl-carbinyl, ##STR4##
In a related patent, U.S. Pat. No. 4,411,925, Brennan, et al.
disclose compounds of the above general formula with R being
defined hereinabove, except R.sup.a is defined as methyl, ethyl,
n-propyl or isopropyl.
U.S. Pat. No. 4,375,430 to Sklavounos discloses dipeptide
sweeteners which are aromatic sulfonic acid salts of
L-aspartyl-D-alaninamides or L-aspartyl-D-serinamides.
European patent application No. 95772 to Tsau describe aspartyl
dipeptide sweeteners of the formula: ##STR5## wherein R' is alkyl
of 1 to 6 carbons, and R.sub.2 is phenyl, phenylakylenyl or
cyclohexylalkenyl, wherein the alkenyl group has 1 to 5 carbons.
Closely related is U.S. Pat. No. 4,439,460 to Tsau, et al. which
describes dipeptide sweeteners of the formula: ##STR6## wherein n
is an integer from 0 to 5, and R.sub.1 is an alkyl, alkylaryl or
alicyclic radical. Similar such compounds are described in many
related patents, the major difference being the definition of
R.sub.2.
In U.S. Pat. No. 3,978,034 to Sheehan, et al., R.sub.2 is defined
as cycloalkenyl or phenyl. U.S. Pat. No. 3,695,898 to Hill defines
R.sub.2 as a mono- or a di-unsaturated alicyclic radical. Haas, et
al. in U.S. Pat. No. 4,029,701 define R.sub.2 as phenyl, lower
alkyl or substituted or unsubstituted cycloalkyl, cycloalkenyl or
cycloalkadienyl, or S(O).sub.m lower alkyl provided that n is 1 or
2 and m is 0 or 2. Closely related are U.S. Pat. Nos. 4,448,716,
4,153,737, 4,031,258, 3,962,468, 3,714,139, 3,642,491, and
3,795,746.
U.S. Pat. No. 3,803,223 to Mazur, et al. describe dipeptide
sweeteners and anti-inflammatory agents having the formula:
##STR7## wherein R is hydrogen or a methyl radical and R' is a
radical selected from the group consisting of alkyl, or ##STR8##
wherein Alk is a lower alkylene radical, X is hydrogen or hydroxy,
and Y is a radical selected from the group consisting of
cyclohexyl, naphthyl, furyl, pyridyl, indolyl, phenyl and
phenoxy.
Goldkamp, et al. in U.S. Pat. No. 4,011,260 describe sweeteners of
the formula: ##STR9## wherein R is hydrogen or a lower alkyl
radical, Alk is a lower alkylene radical and R' is a carbocyclic
radical. Closely related is U.S. Pat. No. 3,442,431.
U.S. Pat. No. 4,423,029 to Rizzi describes sweeteners of the
formula: ##STR10## wherein R is C.sub.4 -C.sub.9 straight, branched
or cyclic alkyl, and wherein carbons a, b and c have the (S)
configuration.
European patent application No. 48,051 describes dipeptide
sweeteners of the formula: ##STR11## wherein M represents hydrogen,
ammonium, alkali or alkaline earth,
R represents ##STR12##
R.sub.1 represents methyl, ethyl, propyl,
R.sub.2 represents -OH, or OCH.sub.3,
* signifies an L-optical configuration for this atom.
German patent application No. 7259426 discloses
L-aspartyl-3-fenchylalanine methyl ester as a sweetening agent.
U.S. Pat. No. 3,971,822 to Chibata, et al., disclose sweeteners
having the formula: ##STR13## wherein R' is hydrogen or hydroxy,
R.sub.2 is alkyl of one to five carbon atoms, alkenyl of two to
three carbon atoms, cycloalkyl of three to five carbon atoms or
methyl cycloalkyl of four to six carbon atoms and Y is alkylene of
one to four carbon atoms.
U.S. Pat. No. 3,907,366 to Fujino, et al. discloses
L-aspartyl-aminomalonic acid alkyl fenchyl diester and its'
physiologically acceptable salts as useful sweeteners. U.S. Pat.
No. 3,959,245 disclose the 2-methyl cyclohexyl analog of the
abovementioned patent.
U.S. Pat. No. 3,920,626 discloses N-.alpha. L-aspartyl derivatives
of lower alkyl esters of O-lower-alkanoyl-L-serine, .beta.-alanine,
.gamma.-aminobutyric acid and D-.beta.-aminobutyric acid as
sweeteners.
Miyoshi, et al. in Bulletin of Chemical Society of Japan, 51, p.
1433-1440 (1978) disclose compounds of the following formula as
sweeteners: ##STR14## wherein R' is H, CH.sub.3, CO.sub.2 CH.sub.3,
or benzyl and R.sub.2 is lower alkyl or unsubstituted or
substituted cycloalkyl.
European patent application No. 128,654 describes gem-diaminoalkane
sweeteners of the formula: ##STR15## wherein m is 0 or 1, R is
lower alkyl (substituted or unsubstituted), R' is H or lower alkyl,
and R" is a branched alkyl, alkylcycloalkyl, cycloalkyl,
polycycloalkyl, phenyl, or alkyl-substituted phenyl, and
physiologically acceptable salts thereof.
U.S. Pat. No. 3,801,563 to Nakajima, et al. disclose sweeteners of
the formula: ##STR16## wherein R' is a branched or cyclic alkyl
group of 3 to 8 carbon atoms, R.sub.2 is a lower alkyl group of 1
to 2 carbon atoms and n is a integer of 0 or 1.
European patent application No. 34,876 describes amides of
L-aspartyl-D-amino acid dipeptides of the formula: ##STR17##
wherein R.sup.a is methyl, ethyl, n-propyl or isopropyl and R is a
branched aliphatic, alicyclic or heterocyclic member which is
branched at the alpha carbon atom and also branched again at one or
both of the beta carbon atoms. These compounds are indicated to be
of significant sweetness.
In the Journal of Medicinal Chemistry, 1984, Vol. 27, No. 12, pp.
1663-8, are described various sweetener dipeptide esters, including
L-aspartyl-.alpha.-aminocycloalkane methyl esters.
The various dipeptide esters of the prior art have been
characterized as lacking significant stability at low pH values
and/or thermal stability. These characterstics have limited the
scope of use of these sweeteners in food products which are of low
pH values or are prepared or served at elevated temperatures.
Accordingly, it is desired to find compounds that provide quality
sweetness when added to foodstuffs or pharmaceuticals at low levels
and thus eliminate or greatly diminish the aforesaid disadvantages
associated with prior art sweeteners.
SUMMARY OF THE INVENTION
The present new compounds are esters of certain
.alpha.-aminodicarboxylic acids and .alpha.-aminoesters which are
low calorie sweeteners that possess a high order of sweetness with
pleasing taste and higher stability at acid pH and elevated
temperatures compared to known dipeptide sweeteners.
This invention provides new sweetening compounds represented by the
formula: ##STR18## and food-acceptable salts thereof, wherein
A is hydrogen, alkyl containing 1-3 carbon atoms, hydroxyalkyl
containing 1-3 carbon atoms or alkoxymethyl wherein the alkoxy
contains 1-3 carbon atoms;
A' is hydrogen or alkyl containing 1-3 carbon atoms;
alternatively
A and A' taken together with the carbon atom to which they are
attached form cycloalkyl containing 3-4 carbon atoms;
Y is --(CHR.sub.2).sub.n --R.sub.1 or --CHR.sub.3 R.sub.4 ;
R.sub.1 is an alkyl-substituted cycloalkyl, cycloalkenyl
bicycloalkyl or bicycloalkenyl wherein at least one alkyl is in the
.beta.-position of the cycloalkyl, cycloalkenyl, bicycloalkyl or
bicycloalkenyl ring, containing up to 7 ring carbon atoms and a
total of 12 carbon atoms;
R.sub.2 is H or alkyl containing 1-4 carbon atoms;
R.sub.3 and R.sub.4 are each cycloalkyl containing 3-4 ring carbon
atoms;
n=0 or 1; and
m=0 or 1, with the proviso that when the double asterisked carbon
is an asymmetric or chiral center, the configuration around said
carbon is in the D form.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the present invention, the preferred compounds
are those in which R.sub.1 is an alkyl-substituted cycloalkyl or
bicycloalkyl containing 5-7 ring carbon atoms and up to a total of
10 carbon atoms. Especially preferred are cycloalkyl substituted
with at least one methyl group on the .beta. and/or .beta.' carbon
atoms of the cycloalkyl ring. Particularly preferred cycloalkyls
include cyclopropyl, cyclopentyl, and cyclohexyl and the preferred
bicycloalkyl is fenchyl.
Also preferred are those compounds in which n=0. In those compounds
in which n=1, R.sub.1 is preferably a cyclopropyl group and R.sub.2
is preferably tertiary butyl, isopropyl or cyclopropyl.
The groups representative of Y in the present new compounds include
such groups as alkyl-substituted cycloalkyls, e.g.,
1,2-dimethylcyclohexyl, 1,2-dimethylcyclopentyl,
1,2-dimethylcycloheptyl, 2,3-dimethylcyclopentyl,
2,3-dimethylcyclohexyl, 2,3-dimethylcycloheptyl,
2,4-dimethylcyclopentyl, 2,4-dimethylcyclohexyl,
2,4-dimethylcycloheptyl, 2,5-dimethylcyclopentyl,
2,5-dimethylcyclohexyl, 2,5-dimethylcycloheptyl,
2,6-dimethylcyclohexyl, 2,6-dimethylcycloheptyl,
2,7-dimethylcycloheptyl, 3,5-dimethylcyclopentyl,
4,5-dimethylcyclopentyl, 4,5-dimethylcycloheptyl,
3,6-dimethylcyclohexyl, 3,7-dimethylcycloheptyl,
4,6-dimethylcyclohexyl, 4,7-dimethylcycloheptyl,
5,6-dimethylcyclohexyl, 5,6-dimethylcyclohexyl,
5,7-dimethylcycloheptyl, 6,7-dimethylcycloheptyl,
2,2-dimethylcyclopentyl, 2,2-dimethylcyclohexyl,
2,2-dimethylcycloheptyl, 2,2,3-trimethylcyclopentyl,
2,2,3-trimethylcyclohexyl, 2,2,3-trimethylcycloheptyl,
2,2,4-trimethylcyclopentyl, 2,2,4-trimethylcyclohexyl,
2,2,4-trimethylcycloheptyl, 2,2,5-trimethylcyclopentyl,
2,2,5-trimethylcyclohexyl, 2,2,5-trimethylcycloheptyl,
2,3,3-trimethylcyclopentyl, 2,3,3-trimethylcyclohexyl,
2,3,3-trimethylcycloheptyl, 2,4,4-trimethylcyclopentyl,
2,4,4-trimethylcyclohexyl, 2,4,4-trimethylcycloheptyl,
1,2,3-trimethylcyclopentyl, 1,2,3-trimethylcyclohexyl,
1,2,3-trimethylcycloheptyl, 1,2,4-trimethylcyclopentyl,
1,2,4-trimethylcyclohexyl, 1,2,4-trimethylcycloheptyl,
1,2,5-trimethylcyclopentyl, 1,2,5-trimethylcyclohexyl,
1,2,5-trimethylcycloheptyl, 1,2,6-trimethylcyclohexyl,
1,2,6-trimethylcycloheptyl, 1,2,7-trimethylcycloheptyl,
2,3,4-trimethylcyclopentyl, 2,3,4-trimethylcyclohexyl,
2,3,4-trimethylcycloheptyl, 2,3,5-trimethylcyclopentyl,
2,3,5-trimethylcyclohexyl, 2,3,5-trimethylcycloheptyl,
2,3,6-trimethylcyclohexyl, 2,3,6-trimethylcycloheptyl,
2,3,7-trimethylcycloheptyl, 2,2,5,5-tetramethylcyclopentyl,
2,2,5,5-tetramethylcyclohexyl, 2,2,5,5-tetramethylcycloheptyl,
2,2,6,6-tetramethylcyclohexyl, 2,2,6,6-tetramethylcycloheptyl,
2,2,7,7-tetramethylcycloheptyl, 2,2,4,4-tetramethylcyclopentyl,
2,2,4,4-tetramethylcyclohexyl, 2,2,4,4-tetramethylcycloheptyl,
2,2,3,3-tetramethylcyclopentyl, 2,2,3,3-tetramethylcyclohexyl,
2,2,3,3-tetramethylcycloheptyl, 1,2,3,4-tetramethylcyclopentyl,
1,2,3,4-tetramethylcyclohexyl, 1,2,3,4-tetramethylcycloheptyl,
1,2,3,5-tetramethylcyclopentyl, 1,2,3,5-tetramethylcyclohexyl,
1,2,3,5-tetramethylcycloheptyl, 1,2,3,6-tetramethylcyclohexyl,
1,2,3,6-tetramethylcycloheptyl, 2,3,4,5-tetramethylcyclopentyl,
2,3,4,5-tetramethylcyclohexyl, 2,3,4,5-tetramethylcycloheptyl,
2,3,4,6-tetramethylcycloheptyl, 2,3,4,6-tetramethylcyclohexyl,
2,3,4,7-tetramethylcycloheptyl, 2,2,3,4-tetramethylcyclopentyl,
2,2,3,4-tetramethylcyclohexyl, 2,2,3,4-tetramethylcycloheptyl,
2,2,3,5-tetramethylcyclopentyl, 2,2,3,5-tetramethylcyclohexyl,
2,2,3,5-tetramethylcycloheptyl, 2,2,3,6-tetramethylcyclohexyl,
2,2,3,6-tetramethylcycloheptyl, 2,2,3,7-tetramethylcycloheptyl,
2,3,3,4-tetramethylcyclohexyl, 2,3,3,4-tetramethylcyclopentyl,
2,3,3,4-tetramethylcycloheptyl, 2,3,3,5-tetramethylcyclopentyl,
2,2,3,5-tetramethylcyclohexyl, 2,3,3,5-tetramethylcycloheptyl,
2,3,3,6-tetramethylcyclohexyl, 2,3,3,6-tetramethylcycloheptyl,
2,3,3,7-tetramethylcycloheptyl, 2,2,3,4-tetramethylcyclopentyl,
2,2,3,4-tetramethylcyclohexyl, 2,3,3,4-tetramethylcycloheptyl,
2,2,3,5-tetramethylcyclopentyl, 2,2,3,5-tetramethylcyclohexyl,
2,2,3,6-tetramethylcyclohexyl, 2,2,3,6-tetramethylcycloheptyl,
2,2,3,7-tetramethylcycloheptyl, 2,2,4,5-tetramethylcyclopentyl,
2,2,4,5-tetramethylcyclohexyl, 2,2,4,5-tetramethylcycloheptyl,
2,2,4,6-tetramethylcyclohexyl, 2,2,4,6-tetramethylcycloheptyl,
2,2,4,7-tetramethylcycloheptyl, dicyclopropylmethyl,
t-butylcyclopropylmethyl, dicyclobutylmethyl,
t-butylcyclobutylmethyl, etc.; -alkyl-substituted cycloalkenes,
e.g., 2-methyl-3-cyclohexenyl, 2-methyl-3-cyclopentenyl,
2-methyl-3-cycloheptenyl, 2-methyl-4-cycloheptenyl,
5-methyl-3-cyclopentenyl, 2-methyl-2-cyclopentenyl,
2-methyl-2-cyclohexenyl, 2-methyl-2-cycloheptenyl,
2-methyl-2-cyclopentenyl, 6-methyl-2-cyclohexenyl,
7-methyl-2-cycloheptenyl, 2,3-dimethyl-2-cyclopentenyl,
2,3-dimethyl-2-cyclohexenyl, 2,4-dimethyl-2-cyclopentenyl,
2,4-dimethyl-2-cyclohexenyl, 2,5-dimethyl-2-cyclohexenyl,
2,5-dimethyl-2-cycloheptenyl, 2,6-dimethyl-2-cyclohexenyl,
2,6-dimethyl-3-cyclohexenyl, 2,5-dimethyl-3-cyclohexenyl,
2,5-dimethyl-2-cyclopentenyl, 2,4-dimethyl-3-cyclopentenyl,
2,4-dimethyl-3-cyclohexenyl, 4,5-dimethylcyclo-3-pentenyl,
5,5-dimethyl-3-cyclopentenyl, 6,6-dimethyl-3-cyclohexenyl,
1,2-dimethyl-3-cyclopentenyl, 1,2-dimethyl-3-cyclohexenyl,
1,5-dimethyl-3-cyclopentenyl, 2,2,6-trimethyl-3-cyclohexenyl,
2,2,5-trimethyl-3-cyclohexenyl, 2,5,5-trimethyl-3-cyclohexenyl,
2,7,7-trimethyl-3-cycloheptenyl, 2,7,7-trimethyl-4-cycloheptenyl,
2,2,7-trimethyl-3-cycloheptenyl, 2,2,7-trimethyl-4-cycloheptenyl,
2,3,6-trimethyl-3-cyclohexenyl, 2,3,7-trimethyl-3-cycloheptenyl,
2,3,5-trimethyl-3-cyclopentenyl,
2,2,6,6-tetramethyl-3-cyclohexenyl,
2,2,5,5-tetramethyl-3-cyclopentenyl,
2,2,7,7-tetramethyl-3-cycloheptenyl,
2,3,5,5-tetramethyl-3-cyclopentenyl,
2,3,6,6-tetramethyl-3-cyclohexenyl,
2,3,7,7-tetramethyl-3-cycloheptenyl,
2,3,6,6-tetramethyl-3-cycloheptenyl,
2,3,5,5-tetramethyl-3-cyclohexenyl,
2,3,4,5-tetramethyl-3-cyclopentenyl,
2,3,4,5-tetramethyl-3-cyclohexenyl, etc.; bicyclic compounds, such
as norbornyl, norcaranyl, norpinanyl, bicyclo[2.2.2]octyl, etc.;
alkyl substituted bicyclic compounds, e.g.,
6,6-dimethyl-bicyclo[3.1.1]heptyl, 6,7,7-trimethylnorbornyl (bornyl
or camphanyl), pinanyl, thujanyl, caranyl, fenchyl,
2-norbornylmethyl, etc.; unsubstituted and alkyl-substituted
bicycloalkenes such as norbornenyl, norpinenyl, norcarenyl,
2-(4-norbornenyl)methyl, pinenyl, carenyl, fenchenyl, etc.; and
tricyclo compounds such as adamentyl and alkyl-substituted
adamantyl, etc.
The preferred R.sub.1 is cycloalkyl or bicycloalkyl or
alkyl-substituted cycloalkyl or bicycloalkyl, especially where the
alkyl group is in the .beta. or .beta.' positions. Further,
preference exists for compounds in which R.sub.1 is a cycloalkyl
with two, three or four alkyl groups in the .beta., .beta.'
positions such as .beta., .beta., .beta.', .beta.'-
tetraelkyl-substituted cyclopentyl, cyclobutyl, cyclohexyl, and
cycloheptyl, as well as .beta., .beta., .beta.'-trialkyl
substituted cyclobutyl, cyclopropyl, cyclohexyl, cyclopentyl, and
cycloheptyl, and fenchyl. Also preferred are
.beta.-alkylcycloalkyls in which the alkyl group is isopropyl or
tertiary butyl.
These novel compounds are effective sweetness agents when used
alone or in combination with other sweeteners in an ingesta, e.g.,
foodstuffs or pharmaceuticals. For example, other natural and/or
artificial sweeteners, which may be used with the novel compounds
of the present invention include sucrose, fructose, corn syrup
solids, dextrose, xylitol, sorbitol, mannitol, acetosulfam,
thaumatin, invert sugar, saccharin, thiophene saccharin,
meta-aminobenzoic acid, metahydroxybenzoic acid, cyclamate,
chlorosucrose, dihydrochalcone, hydrogenated glucose syrups,
aspartame (L-aspartyl-L-phenylalanine methyl ester) and other
dipeptides, glycyrrhizin and stevioside and the like. These
sweeteners when employed with the sweetness agents of the present
invention, it is believed, could produce synergistic sweetness
responses.
Furthermore, when the sweetness agents of the present invention are
added to ingesta, the sweetness agents may be added alone or with
nontoxic carriers such as the abovementioned sweeteners or other
food ingredients such as acidulants, natural and artificial gums,
bulking agents such as polycarbohydrates, dextrins, and other food
approved carbohydrates and derivatives. Typical foodstuffs, and
pharmaceutical preparations, in which the sweetness agents of the
present invention may be used are, for example, beverages including
soft drinks, carbonated beverages, ready to mix beverages and the
like, infused foods (e.g. vegetables or fruits), sauces,
condiments, salad dressings, juices, syrups, desserts, including
puddings, gelatin and frozen desserts, like ice creams, sherbets,
icings and flavored frozen desserts on sticks, confections, chewing
gum, cereals, baked goods, intermediate moisture foods (e.g. dog
food), toothpaste, mouthwash and the like.
In order to achieve the effects of the present invention, the
compounds described herein are generally added to the food product
at a level which is effective to perceive sweetness in the food
stuff and suitably is in an amount in the range of from about
0.0005 to 2% by weight based on the consumed product. Greater
amounts are operable but not practical. Preferred amounts are in
the range of from about 0.001 to about 1% of the foodstuff.
Generally, the sweetening effect provided by the present compounds
are experienced over a wide pH range, e.g., 2 to 10 preferably 3 to
7 and in buffered and unbuffered formulations.
More preferable, if
.alpha.-L-aspartyl-D-alanine[.beta.(+)fenchyl]ester is used as a
sweetener the amount of sweetener can range from about 0.0005 to
about 0.005% by weight of the foodstuff. When
.alpha.-L-aspartyl-2-methylalanine[.beta.(+)fenchyl]ester is used
as a sweetener, the amounts used can fall in a broader range
described above but it is highly preferred to be used in amounts
from about 0.0005 to about 0.01% by weight of the foodstuff.
It is desired that when the sweetness agents of this invention are
employed alone or in combination with another sweetner, the
sweetener or combination of sweeteners provide a sucrose equivalent
in the range of from about 2 weight percent to about 40 weight
percent and more preferably from about 3 weight percent to about 15
weight percent in the foodstuff or pharmaceutical.
A taste procedure for determination of sweetness merely involves
the determination of sucrose equivalency. Sucrose equivalence for
sweeteners are readily determined. The amount of a sweetener that
is equivalent to a given weight percent sucrose can be determined
by having a panel of tasters taste solutions of a sweetener at
known concentrations and match its sweetness to standard solutions
of sucrose.
In order to prepare compounds of the present invention, several
reaction schemes may be employed. In one reaction scheme, compounds
of general formula II (protected .alpha.-aminodicarboxylic acid)
and III (amino-ester compound) are condensed to form compounds of
general formula IV. Subsequent removal of protecting groups B and Z
from compounds of general formula IV give the desired compounds of
general formula I: ##STR19## In these, group Z is an amino
protecting group, B is a carboxyl protecting group, and A, A', Y,
and n have the same meaning as previously described. A variety of
protecting groups known in the art may be employed. Examples of
many of these possible groups may be found in "Protective Groups in
Organic Synthesis" by T. W. Green, John Wiley and Sons, 1981. Among
the preferred groups that may be employed are benzyloxycarbonyl for
A and benzyl for B.
Coupling of compounds with general formula III to compounds having
general formula IV employs established techniques in peptide
chemistry. One such technique uses dicyclohexylcarbodiimide (DCC)
as the coupling agent. The DCC method may be employed with or
without additives such as 4-dimethylaminopyridine or copper (II).
The DCC coupling reaction generally proceeds at room temperature,
however, it may be carried out from about -20.degree. to 50.degree.
C. in a variety of solvents inert to the reactants. Thus suitable
solvents include, but are not limited to, N,N-dimethyl-formamide,
methylene chloride, toluene and the like. Preferably the reaction
is carried out under an inert atmosphere such as argon or nitrogen.
Coupling usually is complete within 2 hours but may take as long as
24 hours depending on reactants.
Various other methods can be employed to prepare the desired
compounds. The following illustrates such methods using aspartic
acid as the amino dicarboxylic acid.
For example, U.S. Pat. Nos. 3,786,039; 3,833,553; 3,879,372 and
3,933,781 disclose the reaction of N-protected aspartic anhydrides
with amino acids and amino acid derivatives to yield the desired
products. These N-protected aspartic anhydrides can be reacted with
compounds of formula III by methods disclosed in the above patents.
As described in U.S. Pat. No. 3,786,039 compounds of formula III
can be reacted directly in inert organic solvents with L-aspartic
anhydride having its amino group protected by a formyl,
carbobenzloxy, or p-methoxycarbobenzloxy group which is
subsequently removed after coupling to give compounds of general
formula I. The N-acyl-L-aspartic anhydrides are prepared by
reacting the corresponding acids with acetic anhydride in amounts
of 1.0-1.2 moles per mole of the N-acyl-L-aspartic acid at
0.degree. to 60.degree. C. in an inert solvent. The
N-acyl-L-aspartic anhydrides are reacted with preferably 1 to 2
moles of compounds of formula III in an organic solvent capable of
dissolving both and inert to the same. Suitable solvents are, but
not limited to ethyl acetate, methyl propionate, tetrahydrofuran,
dioxane, ethyl ether, N,N-dimethylformamide and benzene. The
reaction proceeds smoothly at 0.degree. to 30.degree. C. The N-acyl
group is removed after coupling by catalytic hydrogenation with
palladium on carbon or with HBr or HCl in a conventional manner.
U.S. Pat. No. 3,879,372 discloses that this coupling method can
also be performed in an aqueous solvent at a temperature of
-10.degree. to 50.degree. C. and at a pH of 4-12.
Another method for the synthesis of the desired compounds is the
reaction of compounds of formula III with suitable aspartic acid
derivatives in which protecting groups have been attached to the
amino and beta-carboxy groups and the alpha carboxy group has been
converted to a reactive ester function. As disclosed in U.S. Pat.
No. 3,475,403 these coupled products may be deprotected as
described to yield the desired compounds of formula I.
An alternative scheme to the desired coupled compounds involves
reaction of compounds of formula III with L-aspartic acid
N-thiocarboxyanhydride by the method of Vinick and Jung, Tet.
Lett., 23, 1315-18 (1982). An additional coupling method is
described by T. Miyazawa, Tet. Lett., 25, 771 (1984).
Compounds of general formula III are synthesized using are
recognized techniques. For example, compounds of formula III can be
synthesized by standard esterification methods known in the art by
reacting the free acid or acid functional equivalents, such as
ester or anhydrides, with the corresponding alcohols under
ester-forming conditions, as for example in the presence of mineral
acids, such as hydrochloric or sulfuric acids or organic acids,
such as p-toluene-sulfonic acids. Reaction temperatures are in the
range of -78.degree. to reflux. The reaction is carried out in a
solvent that will dissolve both reactants and is inert to both as
well. Solvents include, but are not limited to methylene chloride,
diethyl ether, tetrahydrofuran, dimethylsulfoxide,
N,N-dimethylformamide, and the like.
With regard to the removal of protecting groups from compounds of
formula IV and N-protected precursors of formula III, a number of
deprotecting techniques are known in the art and can be utilized to
advantage depending on the nature of the protecting groups. Among
such techniques is a catalytic hydrogenation utilizing palladium on
carbon or transfer hydrogenation with 1,4-cyclohexadiene. Generally
the reaction is carried at room temperature but may be conducted
from 5.degree. to 65.degree. C. Usually the reaction is carried out
in the presence of a suitable solvent which may include, but are
not limited to water, methanol, ethanol, dioxane, tetrahydrofuran,
acetic acid, t-butyl alcohol, isopropanol or mixtures thereof. The
reaction is usually run at a positive hydrogen pressure of 50 psi
but can be conducted over the range of 20 to 250 psi. Reactions are
generally quantitative taking 1 to 24 hours for completion.
In any of the previous synethetic methods the desired products are
preferably recovered from reaction mixtures by crystallization.
Alternatively, normal or reverse-phase chromatography may be
utilized as well as liquid/liquid extraction or other means.
The desired compounds of formula I are usually obtained in the free
acid form; they may also be recovered as their physiologically
acceptable salts, i.e., the corresponding amino salts such as
hydrochloride, sulfate, hydrosulfate, nitrate, hydrobromide,
hydroiodide, phosphate or hydrophosphate; or the alkali metal salts
such as the sodium, potassium lithium, or the alkaline earth metal
salts such as calcium or magnesium, as well as aluminum, zinc and
like salts.
Conversion of the free peptide derivatives of formula I into their
physiologically acceptable salts is carried out by conventional
means, as for example, bringing the compounds of formula I into an
alkali metal oxide or carbonate or an alkaline earth metal
hydroxide, oxide, carbonate or other complexed form.
These physiologically acceptable salts can also be utilized as
sweetness agents usually having increased solubility and stability
over their free forms.
It is known to those skilled in the art that the compounds of the
present invention having asymmetric carbon atoms may exist in
racemic or optically active forms. All of these forms are
contemplated within the scope of the invention.
The compounds of the present invention have one asymmetric site,
which is designated by an asterisk (*) in the formula below, and
one pseudoasymmetric site which is designated by a double asterisk
(**). ##STR20## Furthermore, depending upon the substituent, Y may
also contain chiral centers. All of the stereochemical
configurations are encompassed within the above formula. However,
the present invention is directed to compounds of the formula:
##STR21## Although both D and L forms are possible, the present
invention is directed to those compounds in which the dicarboxylic
acid group is in the L-configuration as depicted in Formula I.
Whenever A is identical to A', or A and A' together form an
unsubstituted cyclopropyl or cyclobutyl group, the compounds of the
present invention have at least one asymmetric site, designated by
the asterisk in the dicarboxylic acid moiety.
Whenever the group A and A' are different, the carbon atom
designated by the double asterisk become as asymmetric center and a
chiral center and the compounds of Formula I will contain at least
two asymmetric centers. Furthermore, when A and A' taken together
form a cyclopropyl or cyclobutyl ring having substituents, said
carbon atom designated by the double asterisk may have an
asymmetric center. In those cases wherein the carbon atom
designated by the double asterisk is a chiral center, Formula I
encompasses compounds of Formula II having the L, L configuration
and Formula III having the L, D configuration: ##STR22## In the
instance wherein the carbon designated by the double asterisk is a
chiral center, the preferred compounds are those in which the
configuration around the double asterisked carbon is in the D
configuration. In the production of compounds of Formula I, the L,
L diastereomer though not sweet itself, may be admixed with the L,
D stereoisomers. The admixture of the L, L and L, D stereoisomers
exhibit sweetness, but said mixture is not as sweet as the compound
of Formula III (i.e., the L, D stereoisomer) in its pure form.
The following examples further illustrate the invention. In the
following examples, the sensory evaluation were obtained by a panel
of experts using known weight percent aqueous solutions of the
exemplified compounds and were matched to sucrose standard
solutions.
EXAMPLE 1
L-Aspartyl-D-alanine(2,2,5,5-tetramethyl-1-cyclopentyl)ester
To a magnetically stirred solution of 10 g (0.071 mol)
2,2,5,5-tetramethylcyclopentanone in 75 ml of dry tetrahydrofuran
at 0.degree. C. under argon is added 2.69 g (0.071 mol) of lithium
aluminum hydride. When the reduction was complete, ethyl acetate
was introduced dropwise to destroy unreacted lithium aluminum
hydride. 25 mls of water is then added, followed by 300 mls of
diethyl ether. The organic phase is washed with 100 mls of water,
and dried over MgSO.sub.4. Filtration followed by evaporation
afforded 8.23 g of 2,2,5,5-tetramethylcyclopentanol.
To a stirred solution of 9.59 g (0.043 mol) N-Cbz-alanine in 50 ml
dry CH.sub.2 Cl.sub.2 containing 8.96 g (1 eq.)
dicyclohexylcarbodiimide and 0.4 g dimethylaminopyridine (DMAP),
all at 0.degree. C., is added, via an addition funnel, 6.0 g (0.043
mol) of 2,2,5,5-tetramethylcyclopentanol dissolved in 50 ml
CH.sub.2 Cl.sub.2. After stirring for 48 hours, the mixture is
filtered, and the filtrate is washed with 5% HCl (1.times.50 ml),
saturated NaHCO.sub.3 (1.times.50 ml), and water (1.times.50 ml).
The organic layer is separated, dried over MgSO.sub.4 and
evaporated to yield 5.68 g of crude material, which after silica
gel chromatography yielded 5.68 g of 2,2,5,5-tetramethylcyclopentyl
N-Cbz-D-alanine ester.
5.68 g of 2,2,5,5-Tetramethylcyclopentyl N-Cbz-D-alanine ester is
dissolved in 100 ml CH.sub.3 OH and hydrogenated over 5% Pd/C in a
parr hydrogenation apparatus. When the reaction is complete the
mixture is filtered through Celite and concentrated to yield 3.75 g
of 2,2,5,,5-tetramethylcyclopentyl alanine ester.
To a magnetically stirred solution of 3.75 g (0.017 mol)
2,2,5,5-tetramethylcyclopentyl alanine ester in 170 ml of dry
dimethylformamide at 0.degree. C. under atgon atmosphere is added
6.07 g (0.017 mol) N-Cbz-L-aspartic acid beta-benzyl ester followed
by 2.28 g copper (II) chloride, and 3.54 g
dicyclohexylcarbodiimide. This is stirred for 18 hours, after which
the reaction mixture is poured into 200 ml 0.1 N HCl and extracted
with 300 ml ethyl acetate. The organic phase is washed with
saturated NaHCO.sub.3 and then water, and dried over MgSO.sub.4.
Evaporation of the solvent followed by silica gel chromatography
yielded 5.14 g N-(N'-Cbz-L-aspartyl beta-benzyl ester)-D-alanine
2,2,5,5-tetramethyl-1-cyclopentyl ester.
2.0 g N-(N'-Cbz-L-aspartyl beta-benzyl ester)-D-alanine
2,2,5,5-tetramethyl-1-cyclopentyl ester is dissolved in 50 ml
CH.sub.3 OH and hydrogenated over 5% Pd/C in a Paar apparatus. Upon
completion of the reaction the mixture is filtered and concentrated
to yield 2.59 g L-aspartyl-D-alanine
2,2,5,5-tetramethyl-1-1cyclopentyl ester.
[.alpha.].sub.D.sup.25 (pure)=+21.9.degree..
NMR (DMSO): .delta. 0.8 (s, 6H), 1.00 (s, 6H), 1.3 (d, 3H), 1.45
(s, 4H), 2.2-2.4 (m, 2H), 4.35 (s, 1H), 4.75 (bris).
FAB-MS (m/z): 329 (M-H, 22%), 205 (20%), 90 (17%), 69 (100%).
Sweetness determination with this compound gave the following
results:
______________________________________ SUCROSE CONCENTRATION
EQUIVALENCE ______________________________________ 0.005 2.5 0.010
3.7 0.025 7.7 0.05 8.0 ______________________________________
Similarly, by utilizing the appropriate alcohol, the following
additional compounds are prepared:
N-L-Aspartyl-D-alanine (2,2,5-trimethylcyclopentyl)ester.
N-L-Aspartyl-D-alanine (2,5-dimethylcyclopentyl)ester.
N-L-Aspartyl-D-alanine (dicyclopropylmethyl)ester.
N-L-Aspartyl-D-alanine (fenchyl)ester.
N-L-Aspartyl-D-alanine (2-t-butylcyclopentyl)ester.
N-L-Aspartyl-D-alanine (1-t-butyl-1-cyclopropylmethyl)ester.
N-L-Aspartyl-D-alanine (1-isopropyl-1-cyclopropylmethyl)ester.
EXAMPLE 2
N-(L-Aspartyl)-2-methylalanine(2,2,5,5-tetramethyl-1-cyclopentyl)ester
To a stirred solution of 2 g (0.008 mol) of N-Cbz-2-aminoisobutyric
acid in dry Cl(CH.sub.2).sub.2 Cl containing 1.9 g
dicyclohexylcarbodiimide and 0.1 g dimethylaminopyridine (DMAP),
all at 0.degree. C., is added, via an addition funnel, 1.3 g of
2,2,5,5-tetramethylcyclopentanol dissolved in CH.sub.2 Cl.sub.2.
After stirring for 4 days, the mixture is filtered, and the
filtrate is washed with 5% HCl (1.times.50 ml), saturated
NaHCO.sub.3 (1.times.50 ml), and water (1.times.50 ml). The organic
layer is separated, dried over MgSO.sub.4 and evaporated to yield
N-Cbz-2-aminoisobutyric acid 2,2,5,5-tetramethylcyclopentyl
ester.
N-Cbz-2-aminoisobutyric acid 2,2,5,5-tetramethylcyclopentyl ester
is dissolved in CH.sub.3 OH and hydrogenated over 10% Pd/C in a
Paar hydrogenation apparatus. When the reaction is complete the
mixture is filtered through Celite and concentrated to yield
2-aminoisobutyric acid 2,2,5,5-tetramethylcyclopentyl ester (600
mg).
To a magnetically stirred solution of 0.6 g 2-aminoisobutyric acid
2,2,5,5-tetramethylcyclopentyl ester in 20 ml of dry
dimethylformamide at 0.degree. C. under argon atmosphere was added
1.02 g N-Cbz-L-aspartic acid beta-benzyl ester followed by 0.38 g
of copper (II) chloride and 0.58 g dicyclohexylcarbodiimide. This
is stirred for 18 hours, after which the reaction mixture is poured
into 0.1N HCl and extracted with ethyl acetate. The organic phase
is washed with saturated NaHCO.sub.3 and then water, and dried over
MgSO.sub.4. Evaporation of the solvent yields N-(N'-Cbz-L-Aspartyl
beta-benzyl
ester)-2-methylalanine-(2,2,5,5-tetramethyl-1-cyclopentyl)ester.
N-(N'-Cbz-L-Aspartyl beta-benzyl ester)-2-methylalanine
(2,2,5,5-tetra-methyl-1-cyclopentyl)ester is dissolved in CH.sub.3
OH and hydrogenated over 5% Pd/C in a Parr apparatus. Upon
completion of the reaction the mixture is filtered and concentrated
to yield crude N-(L-Aspartyl)-2-methylalanine
(2,2,5,5-tetramethyl-1-cyclopentyl)ester. Purification of the final
product was done by reverse-phase chromatography on a Whatman
Magnum 20 ODS-3 C.sub.18 column; solvent system: 75% methanol in
H.sub.2 O.
NMR (CDCl.sub.3 /DMSO): .delta.0.90 (s, 6H), 1.00 (s, 6H), 1.25-1.5
(m, 4H), 1.50 (s, 6H), 2.50-2.70 (q. of d., 2H), 3.50, 3.85 (br.s,
1H), 4.85 (br.s).
Sweetness determination with this compound gave the following
results:
______________________________________ SUCROSE CONCENTRATION
EQUIVALENCE ______________________________________ 0.005 2.00 0.010
3.25 0.025 5.75 ______________________________________
Similarly, by utilizing the appropriate alcohol, the following
additional compounds are prepared:
N-L-Aspartyl 2-methylalanine (2,2,5-trimethylcyclopentyl)ester.
N-L-Aspartyl 2-methylalanine(2,5-dimethylcyclopentyl)ester.
N-L-Aspartyl 2-methylalanine(dicyclopropylmethyl)ester.
N-L-Aspartyl 2-methylalanine(fenchyl)ester.
N-L-Aspartyl 2-methylalanine(2-t-butylcyclopentyl)ester.
N-L-Aspartyl
2-methylalanine(1-t-butyl-1-cyclopropylmethyl)ester.
N-L-Aspartyl
2-methylalanine(1-isopropyl-1-cyclopropylmethyl)ester.
EXAMPLE 3
N-(L-Aspartyl)-1-amino-1-cyclopropanecarboxylic acid
(2,2,5,5-tetramethyl-1-cyclopentyl)ester
To a stirred solution of N-Cbz-1-aminocyclopropane carboxylic acid
in dry (CH.sub.2).sub.2 Cl.sub.2 containing
dicyclohexylcarbodiimide and dimethylaminopyridine (DMAP), all at
0.degree. C., is added, via an addition funnel,
2,2,5,5-tetramethylcyclopentanol dissolved in CH.sub.2 Cl.sub.2.
After stirring for 4 days, the mixture is filtered, and the
filtrate is washed with 5% HCl (1.times.50 ml), saturated
NaHCO.sub.3 (1.times.50 ml), and water (1.times.50 ml). The organic
layer is separated, dried over MgSO.sub.4 and evaporated to yield
N-Cbz-1-aminocyclopropanecarboxylic acid
2,2,5,5-tetramethylcyclopentyl ester.
N-Cbz-1-aminocyclopropanecarboxylic acid
2,2,5,5-tetramethylcyclopentyl ester is dissolved in absolute
alcohol at 0.degree. C. in an ultrasound bath. Palladium on carbon
(10%) is added. The hydrogen source, 1,4-cyclohexadiene, is added,
and ultrasound is commenced for eight minutes. The slurry is then
filtered through a bed of Celite with ethyl alcohol. The solvent is
removed by rotary evaporation to yield 1-aminocyclopropylcarboxylic
acid 2,2,5,5-tetramethylcyclopentyl ester.
To a magnetically stirred solution of 1-aminocyclopropane
carboxylic acid 2,2,5,5-tetramethylcyclopentyl ester in dry
dimethylformamide at 0.degree. C. under argon atmosphere is added
N-Cbz-L-aspartic acid beta-benzyl ester followed by copper (II)
chloride and dicyclohexylcarbodiimide. This is stirred for 18
hours, after which the reaction mixture is poured into 0.1N HCl and
extracted with ethyl acetate. The organic phase is washed with
saturated NaHCO.sub.3 and then water, and dried over MgSO.sub.4.
Evaporation of the solvent yields N-(N'-Cbz-L-Aspartyl beta-benzyl
ester)-1-amino-1-cyclopropanecarboxylic acid
2,2,5,5-tetramethyl-1-cyclopentyl ester.
The N-(N'-Cbz-L-Aspartyl-beta-benzyl
ester)-1-amino-1-cyclopropanecarboxylic acid
2,2,5,5-tetramethyl-1-cyclopentyl ester is dissolved in absolute
alcohol at 0.degree. C. in an ultrasound bath. Palladium on carbon
(10%) is added. The hydrogen source, 1,4-cyclohexadiene, is added,
and ultrasound is commenced for eight minutes. The slurry is then
filtered through a bed of Celite with ethyl alcohol. The solvent is
removed by rotary evaporation to afford the final product.
Similarly, by utilizing the appropriate starting materials the
following additional compounds are prepared:
N-L-aspartyl 1-aminocyclopropane-1-carboxylic
acid(2,2,5,-trimethylcyclopentyl)ester.
N-L-aspartyl 1-aminocyclopropane-1-carboxylic acid(2,5-
dimethylcyclopentyl)ester.
N-L-aspartyl 1-aminocyclopropane-1-carboxylic
acid(dicyclopropylmethyl)ester.
N-L-aspartyl 1-aminocyclopropane-1-carboxylic
acid(fenchyl)ester.
N-L-aspartyl 1-aminocyclopropane-1-carboxylic
acid(2-t-butylcyclopentyl)ester.
N-L-aspartyl 1-aminocyclopropane-1-carboxylic
acid(1-t-butyl-1-cyclopropylmethyl)ester.
N-L-aspartyl 1-aminocyclopropane-1-carboxylic
acid(1-isopropyl-1-cyclopropylmethyl)ester.
The sweetness determination with
L-Aspartyl-1-aminocyclopropyl-1-carboxylic acid,
2,5-dimethyl-1-cyclopentyl ester gave the following results:
______________________________________ Sweetness relative to
Sucrose % Compound Sucrose Equivalents (.times. Sucrose)
______________________________________ 0.005 1.0 200 0.010 2.2 217
0.025 3.3 133 ______________________________________
EXAMPLE 4
N-L-Aspartyl-O-methyl-D-serine(2,2,5,-trimethylcyclopentyl)ester
To a solution of 5 g N-Cbz-D-serine 2,2,5-trimethylcyclopentyl
ester in 50 ml dry CH.sub.2 Cl.sub.2 is added 2 equivalents of
Ag.sub.2 O and 2 equivalents of methyl iodide. After stirring for 2
hours, the mixture is filtered and concentrated to yield the methyl
ether of N-Cbz-D-serine 2,2,5,-trimethylcyclopentyl ester. 3 g of
N-Cbz-D-serine methyl ether 2,2,5-trimethylcyclopentyl ester is
hydrogenated over 0.5 g 10% Pd/C in 100 ml CH.sub.3 OH. Upon
completion, the mixture is filtered and concentrated to yield
3-methoxy-D-alanine 2,2,5-trimethylcyclopentyl ester. To a
magnetically stirred solution of 2 g of 3-methoxy-D-alanine
2,2,5-trimethylcyclopentyl ester in 100 ml DMF at 0.degree. C. is
added 1 equivalent of N-Cbz-L-aspartic acid-.beta.-benzyl ester
followed by addition of 1 equivalent each of Cu(II) chloride and
dicyclohexylcarbodiimide. After 18 hours the mixture is poured into
200 ml 0.1N HCl and extracted with 300 ml ethyl acetate. The
organic phase is washed with saturated NaHCO.sub.3, and H.sub.2 O,
dried over MgSO.sub.4, filtered and concentrated to an oil that is
reconstituted in 50 ml CH.sub.3 OH and hydrogenated over 0.5 g 5%
Pd/C. Filtration followed by concentration yields
L-aspartyl-D-serine 2,2,5-trimethylcyclopentyl ester methyl
ether.
Using the appropriate starting materials, the following dipeptides
are additionally prepared:
N-L-Aspartyl-O-methyl-D-serine(2,5-dimethylcyclopentyl)ester.
N-L-Aspartyl-O-methyl-D-serine(dicyclopropylmethyl)ester.
N-L-Aspartyl-O-methyl-D-serine(fenchyl)ester.
N-L-Aspartyl-O-methyl-D-serine(2-t-butylcyclopentyl)ester.
N-L-Aspartyl-O-methyl-D-serine(1-t-butyl-1-cyclopropylmethyl)ester.
N-L-Aspartyl-O-methyl-D-serine(1-isopropyl-1-cyclopropylmethyl)ester.
N-L-Aspartyl-O-methyl-D-serine(2,2,5,5-tetramethylcyclopentyl)ester.
EXAMPLE 5
L-Aspartyl-D-serine-(2,2,5-trimethylcyclopentyl)ester
Into a suspension of N-Cbz-D-serine (5 g) in 50 ml of dry THF
containing 1 equivalent of 2,2,5-trimethylcyclopentanol is bubbled
dry hydrogen chloride gas at room temperature. Upon complete
solution of the mixture, the reaction is refluxed for 5 hours, then
concentrated. Ethyl acetate is added, and this is washed with
saturated sodium bicarbonate, water, and dried over MgSO.sub.4.
Filtration followed by concentration yields
N-Cbz-D-serine-2,2,5-trimethylcyclopentyl ester. 5 g of this
product is dissolved in 10 ml methanol and hydrogenated in a Paar
apparatus over 1 g of 5% Pd/C to yield
2,2,5-trimethylcyclopentyl-D-serinate.
To a magnetically stirred solution of 0.1 mole
2,2,5-trimethylcyclopentyl-D-serinate in 100 ml dry DMF at
0.degree. C. under an argon atmosphere is added 1 equivalent of
N-Cbz-L-aspartic acid .beta.-benzyl ester followed by addition of 1
equivalent each of Cu(II) chloride and dicyclohexylcarbodiimide.
After 18 hours the mixture is poured into 200 ml 0.1N HCl and
extracted with 300 ml ethyl acetate which is successively washed
with saturated NaHCO.sub.3, H.sub.2 O, and dried over MgSO.sub.4.
Filtration and evaporation yields
N-Cbz-.beta.-benzyl-L-aspartyl-D-serine 2,2,5-trimethylcyclopentyl
ester. 2 g N-Cbz-.beta.-benzyl-L-aspartyl-D-serine
2,2,5-trimethylcyclopentyl ester in 50 ml dry CH.sub.3 OH is
hydrogenated in a Paar apparatus over 5% Pd/C. Upon completion of
the reaction, the mixture is filtered through Celite and
concentrated to dryness to yield the final product.
Similarly, utilizing the appropriate starting materials the
following additional compounds are prepared:
N-L-Aspartyl-D-serine(2,2,5-trimethylcyclopentyl)ester.
N-L-Aspartyl-D-serine(2,5-dimethylcyclopentyl)ester.
N-L-Aspartyl-D-serine(dicyclopropylmethyl)ester.
N-L-Aspartyl-D-serine(fenchyl)ester.
N-L-Aspartyl-D-serine(2-t-butylcyclopentyl)ester.
N-L-Aspartyl-D-serine(1-t-butyl-1-cyclopropylmethyl)ester.
N-L-Aspartyl-D-serine(1-isopropyl-1-cyclopropylmethyl)ester.
N-L-Aspartyl-D-serine-(2,2,5,5-tetramethylcyclopentyl)ester.
EXAMPLE 6
N-L-Aspartyl-D-alanine(1-methyl-1-cyclopentyl)ester
A. N-carbobenzoxy-D-alanine(1-methyl-1-cyclopentyl)ester
To a magnetically stirred solution of 22.3 g (0.1 mol)
N-Cbz-D-alanine in 50 mls of dry dichloromethane containing 0.5 mls
of concentrated sulfuric acid at 0.degree. C., was added dropwise a
10 g (0.1 mol) sample of 1-methylcyclopentene in 50 mls of
dichloromethane. After 5 days of stirring at room temperature, the
mixture was heated to reflux for 4 hours, after which the reaction
was cooled to room temperature, washed with 100 mls of saturated
NaHCO.sub.3, 100 mls of water and dried over MgSO.sub.4. Filtration
followed by evaporation of the solvent yielded 1.81 g of the
product.
NMR(CDCl.sub.3): .delta.1.3-1.4 (d, 3H), 1.5 (s, 3H), 1.5-1.7 (m,
8H), 4.2 (m, 1H), 5.05 (s, 2H), 5.25 (m, 1H), 7.3 (s, 5H).
B. D-Alanine(1-methylcyclopentyl)ester
1.8 g of the compound of part A was hydrogenated in 50 mls of
methanol containing 0.5 g of 5% Pd/C catalyst in a Paar apparatus.
The catalyst was filtered off, the solvent was removed by
evaporation and 0.54 g of 1-methylcyclopentyl D-alanine ester was
obtained.
C.
Beta-benzyl-N-carbobenzoxy-L-aspartyl-D-alanine-(1-methyl-1-cyclopentyl)es
ter
To 0.54 g (0.0031 mol) of the product from B in 31 mls of
dimethylformamide at 0.degree. C. under an argon atmosphere is
added 1.11 g (0.0031 mol) of N-Cbz-L-aspartic acid, betabenzyl
ester, followed by 417 mg (1 equiv.) Cu(II)Cl.sub.2 and 646 mg. (1
equiv.) dicyclohexylcarbodimide. This is stirred for 16 hours,
after which it is poured into 200 mls of 0.1N HCl and extracted
with 3.times.100 ml of ethyl acetate. The organic phase was washed
with 100 ml of water and dried over MgSO.sub.4. Filtration and
evaporation of the solvent yielded 1.0 g of
beta-benzyl-N-carbobenzoxy
L-aspartyl-D-alanine-(1-methyl-1-cyclopentyl)ester.
NMR (CDCl.sub.3): .delta.1.3-1.4 (d, 3H), 1.5 (s, 3H), 1.5-1.7 (m,
8H), 2.7-3.0 (d of d, 2H), 4.35 (m, 2H), 5.1 (s, 2H), 5.8 (d, 1H),
6.9 (d, 1H), 7.3 (s, 5H).
D. N-L-aspartyl-D-alanine(1-methyl-1-cyclopentyl)ester
2.3 g of the product from C was hydrogenated over 0.5 g of Pd/C
(5%) in methanol to yield 280 mg.
L-aspartyl-D-alanine(1-methyl-1-cyclopentyl)ester.
NMR (D.sub.2 O): .delta.1.3-1.4 (d, 3H), 1.5 (s, 3H), 1.5-1.7 (m,
8H), 2.3 (m, 2H), 4.2 (m, 2H).
Sweetness determination with this compound gave the following
results:
______________________________________ Sweetness Value Percent of
Relative to Compound Sucrose Equivalence Sucrose (.times. Sucrose)
______________________________________ 0.05 2.0 40
______________________________________
EXAMPLE 7
N-L-Aspartyl-D-alanine(2,5-dimethylcyclopentyl)ester
A. N-carbobenzoxy-D-alanine(2,5-dimethylcyclopentyl)ester
To a magnetically stirred solution of 19.63 g (0.088 mol)
N-Cbz-D-alanine, 18.34 g (1 equiv.) of dicyclohexylcarbodiimide,
and 0.88 g of 4-(dimethylamino)pyridine in 150 mls of
dichloromethane at 0.degree. C., is added 10 g (0.088 mol) of
2,5-dimethylcyclopentanol. After 48 hours, the reaction mixture is
filtered to remove dicyclohexylurea and concentrated to a pale
yellow oil, which is redissolved in ethyl acetate. This is
successively washed with 100 mls of 5% HCl, 100 mls of saturated
NaHCO.sub.3, 100 mls of saturated NaCl and 100 mls of water, dried
over MgSO.sub.4 and filtered. Evaporation of the solvent afforded
23.7 g of N-Cbz-D-alanine, 2,5-dimethylcyclopentylester.
B. D-Alanine-(2,5-dimethylcyclopentyl)ester
5.08 g of the product from A was hydrogenated several times over
0.5 g of 5% Pd/C in 50 mls of CH.sub.3 OH to yield 2.59 g of
D-alanine-(2,5-dimethylcyclopentyl)ester.
C.
N-Cbz-beta-benzyl-L-aspartyl-D-alanine(2,5-dimethylcyclopentyl)ester
To a solution of 9.45 g (0.05 mol) of the product from B in 300 mls
of dry DMF at 0.degree. C. is added 17.85 g (1 eq.) of
N-Cbz-beta-benzyl-L-aspartic acid, 6.72 g (1 eq.)
copper(II)chloride and 10.42 g (1 eq.) dicyclohexylcarbodiimide.
This, at 0.degree. C. under an argon atmosphere, is stirred for 18
hours. The mixture is filtered to remove the urea, and is poured
onto 300 mls of 0.1N HCl. The blue solution is extracted with
3.times.200 ml of diethyl ether and 3.times.200 ml of ethyl
acetate. The combined organic phases were washed with 100 mls of
NaHCO.sub.3 (saturated), 100 mls of saturated NaCl, and 100 mls of
water, and dried over MgSO.sub.4. Filtration and evaporation
afforded 29.6 g of the crude above-identified product, which was
purified by flash silica gel chromatography.
D. N-L-Aspartyl-D-alanine(2,5-dimethylcyclopentyl)ester
The product from C was hydrogenated in the usual fashion in
methanol over 5% Pd/C to yield the final product.
[.alpha.].sub.D.sup.25 =2.7.degree..
Sweetness determination with this compound gave the following
results:
______________________________________ Sweetness relative to
Sucrose Concentration Sucrose Equivalence (.times. Sucrose)
______________________________________ 0.005 1.16 233 0.01 2.3 230
0.025 4.82 193 0.050 7.50 150
______________________________________
EXAMPLE 8
N-L-Aspartyl-1-aminocyclopropane carboxylic acid
(2,2,5,5-tetramethyl-1-cyclopentyl)ester
A. N-t-butoxycarbonyl-1-aminocyclopropanecarboxylic acid (1)
To a solution of 1-aminocyclopropanecarboxylic acid (3.03 g) in
saturated aqueous sodium bicarbonate (150 ml) was added a solution
of di-t-butyldicarbonate (9.82 g) in t-butanol (60 ml), and the
resulting mixture was stirred overnight. Water was then added and
the mixture was washed with ethyl acetate. The aqueous phase was
separated, made acid to pH 1 with concentrated hydrochloric acid
and extracted twice with ethyl acetate. The combined extracts were
washed with saturated sodium chloride, dried over magnesium
sulfate, and the solvent was evaporated to yield a white solid.
(4.77 g, 86%).
NMR (CDCl.sub.3): .delta.1.05-1.35 (m, 2H, cyclopropyl), 1.41 (s,
9H, t-butyl), 1.41-1.70 (m, 2H, cyclopropyl), 5.20, (br. s, 1H,
NH), 9.25 (br. s, 1H, CO.sub.2 H).
B. 2,5-Dimethylcyclopentyl
N-t-butoxycarbonyl-1-aminocyclopropanecarboxylate (2)
To a solution of 2,5-dimethylcyclopentanol (0.55 g), compound 1
(0.97 g), and 4-(dimethylamino)pyridine (0.06 g.) in methylene
chloride (100 ml) was added dicyclohexylcarbodiimide (1.09 g.), and
the resulting mixture was stirred overnight. The precipitated
dicyclohexylurea was removed by filtration, and the filtrate was
evaporated. Ethyl acetate was then added to the residue, and the
mixture was filtered again. The filtrate was washed with 1M
hydrochloric acid, saturated aqueous sodium bicarbonate, and water,
dried over magnesium sulfate, and the solvent was evaporated to a
colorless oil (1.18 g. 83%). The product was purified by column
chromatography on silica gel, 4:1 hexane:ethyl acetate, eluent.
NMR (CDCl.sub.3): .delta.0.92 (t, 6H, 2CH.sub.3), 1.05-2.10 (m,
10H, cyclopentyl, cyclopropyl), 1.40 (s, 9H, t-Bu), 4.60 (dd., 1H,
CO.sub.2 CH), 5.05 (br. s, 1H, NH).
C.
.beta.-Benzyl-N-benzyloxycarbonyl-L-aspartyl-1-aminocyclopropanecarboxylic
acid, 2,5-dimethylcyclopentyl ester (3)
A mixture of compound 2 (0.57 g), 95% ethanol (11 ml), water (7.5
mls) and concentrated hydrochloric acid (4 ml) was heated to reflux
for 2 hours. The mixture was cooled, and 1 molar hydrochloric acid
was added. The solution was washed with ethyl acetate. The
separated aqueous phase was made basic with 1M sodium hydroxide and
extracted twice with ethyl acetate. The combined extracts were
washed with saturated sodium chloride, dried over magnesium
sulfate, and the solvent was evaporated to yield 0.22 g of a
colorless oil. Dicyclohexylcarbodiimide (0.25 g) was added to a
solution of the above oil, followed by
N-benzyloxycarbonyl-L-aspartic acid, beta-benzyl ester (0.40 g) and
copper(II)chloride (0.17 g) in dimethyl formamide (10 mls). The
resulting mixture was stirred overnight. The green mixture was then
filtered to remove dicyclohexylurea, and 1M hydrochloric acid was
added to the filtrate. This was extracted twice with ethyl acetate,
and the combined extracts were washed with 1M hydrochloric acid,
saturated sodium bicarbonate and saturated sodium chloride. The
solution was dried over magnesium sulfate, and the solvent was
evaporated to give 0.53 g of a yellow oil. This is purified by
column chromatography on silica gel, 4:1 hexane:ethyl acetate,
eluent, to give the desired product as a white solid (0.33 g,
32%).
NMR (CDCl.sub.3): .delta.0.91 (t, 6H, 2CH.sub.3), 0.80-2.25 (m,
10H, cyclopropyl, cyclopentyl), 2.70 (dd., 1H, J.sub.1 =7 Hz,
J.sub.2 =17 Hz, aspartyl CH.sub.2), 3.00 (dd., 1H, J.sub.1 =5 Hz,
J.sub.2 =17 Hz, aspartyl CH.sub.2), 4.30-4.70 (m, 2H, CO.sub.2 CH,
aspartyl CH), 5.10 (s, 4H, 2PhCH.sub.2), 5.87 (br. d, 1H, NH), 6.95
(br. s, 1H, NH), 7.30 (s, 10H, 2Ph).
D. L-Aspartyl 1-aminocyclopropanecarboxylic acid,
2,5-dimethylcyclopentyl ester
A mixture of compound 3 (0.31 g), 1,4-cyclohexadiene (0.46 g), 10%
palladium-on-carbon (0.3 g) and 95% ethanol (10 ml) was placed in
an ultrasonic bath for 10 minutes. The mixture was then filtered
through Celite, and the solvent was evaporated to yield 130 mg of a
colorless oil which solidified upon standing. This was purified by
HPLC using a reverse phase C.sub.18 column, 60% methanol in water
as eluent to yield the desired product as a white solid (72 mg,
40%).
MP: 155.5.degree.-157.degree. C.
FAB MS (m/z): 313 (M+H, 22%) 217 (87%), 102 (69%), 88 (100%).
EXAMPLE 9
.alpha.-L-Aspartyl-2-methylalanine[.beta.(+)Fenchyl]ester
N-CBZ-protected amino isobutyric acid (Chemical Dynamics, Inc.) was
dissolved in 1,2-dichloroethane (50 mL) at 0.degree. C. under
argon. A solution of N,N-dimethylaminopyridine (0.5 equiv.) and
.beta.(+)fenchyl alcohol (1 equiv.) in 1,2-dichloroethane (10 mL)
was added. Lastly, dicyclohexylcarbodiimide (1.1 equiv.) was added
as a solid. After five days of stirring at room temperature the
urea was removed by filtration and the filtrate was diluted with
petroleum ether (50 mL). The solution was clarified again by
filtration and the filtrate was hi-vacuum rotary evaporated to a
paste. Column chromatography on silica gel with 15:1 petroleum
ether/ethyl acetate gave the pure product in 75-79% yield as a
white crystalline solid.
NMR (CDCl.sub.3): .delta.0.90 (s, 3H), 1.05 (s, 3H) 1.10 (s, 3H),
1.20-1.80 (m, 7H), 1.60 (s, 6H), 4.20 (s, 1H), 5.10 (s, 2H), 5.55
(s, 1H), 7.40 (s, 5H).
[.alpha.].sub.D.sup.25 =-11.65.degree. (MeOH) mp.
83.degree.-85.degree. C. The ester from above was deprotected in
the usual manner by hydrogenation with palladium on carbon (10%) in
methanol to give a quantitative yield of the free-amino ester.
The amine was immediately dissolved in DMF and coupled to an
aspartic acid precursor by the Copper(II)chloride procedure to give
a 90% yield of N-CBZ.alpha.-L-aspartic acid
.beta.-benzylester.alpha.2-methylalanine[.beta.(+)Fenchyl]ester.
NMR(CDCl.sub.3): .delta.0.90 (s, 3H), 1.05 (s, 3H), 1.10 (s, 3H),
1.20-1.80 (m, 7H), 1.6 (d, 6H) 2.70-3.15 (m, 2H), 4.1-4.2 (m, 1H),
4.20 (s, 1H), 4.60 (s, 1H), 5.10 (s, 4H), 5.60 (d, 1H), 5.90 (d,
1H), 5.90 (d, 1H), 7.40 (s, 10H).
The product was deprotected by hydrogenation and purified by Rp
C.sub.18 column chromatography with 85:15 methanol:water eluant,
[.alpha.].sub.D.sup.25 =-3.30.degree. (MeOH) mp.
121.degree.-3.degree. C.
Sweetness determination with this compound gave the following
results:
______________________________________ Sweetness relative to
Concentration Sucrose Equivalence Sucrose (.times. Sucrose)
______________________________________ 0.00750 8.5% 1133 0.00375
6.0% 1600 0.00185 5.7% 3100 0.00692 3.5% 3800 0.0025 6.0% 2400
0.0025 4.3% 1733 0.0025 4.25% 1700 0.005 7.37% 1475 0.005 7.0% 1400
0.005 6.0% 1200 0.01 9.25% 925 0.01 9.0% 900
______________________________________
EXAMPLE 10
.alpha.-L-Aspartyl-D-alanine[.beta.(+)Fenchyl]ester
A. exo-.beta.-(+)-Fenchol
To a refluxing suspension of 72.65 g aluminum isopropoxide in 300
ml of freshly distilled isopropyl alcohol, was added dropwise, 27.1
g R-(-)-fenchone in 50 ml isopropanol. The reaction was halted
after six days when it was determined by gas chromatography
(Carbowax 20 M) that more than 50% of the ketone was reduced. It
was also determined by capillary chromatography (Supelcowax 10)
that the exo/endo ratio for the fenchol was 3/1. Upon cooling, the
mixture was filtered and washed thoroughly with dichloromethane.
The pecipitate was dissolved in 5% HCl (100 ml) and extracted with
dichloromethane (50 ml). The combined dichloromethane solutions
were washed with 5% HCl (50 ml), saturated NaHCO.sub.3 (50 ml) and
water (50 ml) and dried over MgSO.sub.4. Filtration and removal of
the solvent afforded 23.44 g of an oil that was 40% unreacted
fenchone and 60% .alpha. and .beta. fenchol isomers.
A mixture of 12 g (0.78 mol) .beta. and .alpha.-fenchols, 11.9 ml
(1.1 eq) triethylamine and 15.9 g p-nitrobenzoyl chloride (1.1 g)
in 500 mls dry dichlormethane was refluxed for 24 hours. The
mixture of .beta./.alpha. esters was separated by silica gel flash
chromatography using hexane:ethyl acetate (40:1). 6.0 g of the
exo-fenchyl para-nitrobenzate was isolated. ([.alpha.].sub.D.sup.25
=-17.1.degree. (in benzene). 3 g of fenchol (9/1; .beta./.alpha.)
was obtained upon basic hydrolysis of the nitrobenzate ester
(refluxing excess NaOH in methanol). .beta.-(+)-fenchol;
[.alpha.].sub.D.sup.25 =+23.4.degree. (neat),
NMR: .delta.0.95-1.8 (16H, m, CH.sub.2, CH.sub.3); 3.0 ppm (1H, s,
CH-O).
B. N-Cbz-D-alanine, .beta.-(+)-fenchyl ester
To a stirred solution of 1.3 g .beta.-(+)-fenchol in 20 ml dry
dichloromethane was added 1.9 g (0.0084 mol) N-Cbz D-alanine, and
the solution was cooled to 0.degree. C. Then, 0.113 g
p-dimethylaminopyridine and 1.91 g dicyclohexylcarbodiimide were
added. After 24 hours, the reaction was stopped and filtered. The
solvent was evaporated and the oily residue was dissolved in
diethyl ether, washed with 5% HCl (25 ml), saturated NaHCO.sub.3
(25 ml), water (25 ml) and dried over MgSO.sub.4. After filtration
and solvent evaporation, the product was purified by silica gel
chromatography to yield 1.86 g N-Cbz-D-alanine, .beta.-(+)-fenchyl
ester; [.alpha.].sub.D.sup.25 =+3.86.degree..
NMR: .delta.0.8-1.8 ppm (19H, m, CH.sub.2, CH.sub.3); 4.2 ppm (1H,
s, CH-O); 4.4 ppm (1H, m, ##STR23## 5.1 ppm (2H, s, CH.sub.2 -Ph)
5.4 ppm (1H, d, NH); 7.4 ppm (5H, s, Ph). C. D-alanine,
.beta.(+)-fenchyl ester
The N-Cbz-D-alanine, .beta.-(+)-fenchyl ester, (1.86 g) was
dissolved in 50 ml methanol and hydrogenated over 0.1 g 5% Pd/C in
a Paar shaker. After 2 hours the reaction was over; it was filtered
through Celite, washed with methanol, concentrated and the
crystallized residue was dissolved in dichloromethane.
D. N-Cbz-.beta.-benzyl-L-aspartyl-D-alanine, .beta.-(+)fenchyl
ester
To the DMF solution containing the D-alanine ester (0.00355 mol)
was added an equimolar amount of B-benzyl-N-Cbz-L-aspartic acid
(1.27 g) and 0.526 g Cu(II)Cl.sub.2. Upon solution of the
CuCl.sub.2, DCC (0.81 g) was added. After 24 hours, the reaction
was complete, the urea was filtered and the solvent was evaporated.
The yellow oil was dissolved in diethyl ether (25 ml) and washed
with 5% HCl (25 ml), saturated NaHCO.sub.3 (25 ml), and H.sub.2 O
(25 ml). The ether layer was dried over MgSO.sub.4 and evaporated
to yield 0.95 g of product.
NMR: .delta.0.85- 1.80 (19H, m, CH.sub.2, CH.sub.3), 4.2 ppm (1H,
s, CH-O); 4.5-4.7 ppm (2H, m, ##STR24## 5.1 ppm (4H, s, OCH.sub.2
-Ph); 5.95 ppm (1H, d, NH); 7.05 ppm (1H, d, NH); 7.4 ppm (10H, s,
Ph).
E. L-aspartyl-D-alanine, .beta.-(+)-fenchyl ester
0.95 g protected dipeptide was dissolved in 50 ml methanol to which
0.1 g 10% Pd/C was added. This was hydrogenated in Paar shaker for
2 hours. The solution was filtered and evaporated to dryness to
yield 0.194 g solid; [.alpha.].sub.D.sup.25 =-0.867.degree..
The product was purified on reverse phase HPLC (85% methanol/water)
to yield 75 mg L-aspartyl-D-alanine, .beta.-(+)Fenchyl ester.
NMR: .delta.0.8-1.8 (19H, m, CH.sub.2, CH.sub.3); 2.3-2.4 ppm (2H,
m, ##STR25## 4.2 ppm (1H, s, OCH); 4.5 ppm (2H, m, N-CH); 8.8 ppm
(1H, s, ##STR26##
Sweetness determination with this compound gave the following
results:
______________________________________ Sweetness relative to
Concentration Sucrose Equivalence Sucrose (.times. Sucrose)
______________________________________ 0.00012 0.6% 5000 0.00024
1.42% 5900 0.00047 2.28% 4900 0.00092 4.7% 5100 0.00185 6.5% 3500
0.0025 6.0% 2400 0.00375 8.6% 2300 0.005 9.3% 1860 0.005 10.0% 2000
0.0075 9.0% 1200 0.01 11.0% 1100
______________________________________
The compounds of this invention possess greater sweetness and
higher stability in comparison to corresponding esters of the prior
art.
EXAMPLE 11
.alpha.-L-Aspartyl-2-methylalanine[.beta.(+)Fenchyl]ester
(Example 9), .alpha.-L-Aspartyl-D-alanine[.beta.(+)Fenchyl]ester,
(Example 10) and aspartame L-Aspartyl-L-phenylalanine methyl ester
were studied for stability at pH3, 5 and 7 in buffer solutions
maintained at 50.degree. C., 75.degree. C., or 100.degree. C. the
following results were obtained:
______________________________________ pH 3 pH 5 pH 7
______________________________________ Half Life hours at
100.degree. C. Example 9 8.4 33 67 Example 10 3.9 14 10 Aspartame
5.3 5.3 <<1 Half Life, days at 75.degree. C. Example 9 3.0
15.0 Example 10 1.3 5.1 Aspartame 0.9 1.1 Half Life, days at
50.degree. C. Example 9 64 150 Example 10 22 131
______________________________________
The sweeteners of Example 9 and Example 10 have outstanding
stability in buffered solutions at pH's 3, 5, and 7. Example 9 and
Example 10 have better stability in the buffered solutions studied
than does aspartame, except at pH 3 @ 100.degree. C. where
aspartame has an intermediate stability between Example 9 and
Example 10. The composition of Example 9 is more stable than the
composition Example 10. The half life of Example 9 is 2 to 3 times
longer in buffered solutions at 75.degree. C. and 100.degree. C. at
pH 3 and pH 5 than Example 10. The half life of Example 9 in a
buffered solution at 50.degree. C. and a pH 5 is about 1.1 to about
2.9 times longer than that of Example 10.
* * * * *